Method for emulsifying polymerizable compounds and effecting polymerization with the emulsions



Patented Oct. 13 1953 METHOD FOR EMULSIFYING POLYMERIZ- Y ABLE COMPOUNDS AND EFFECTING POLY- I, l MERIZATION WITH THE EMULSIONS jack Adams, Midland, Mich., assignor to The Dow Chemical Company, Midland, Micln, a

corporation of Delaware No Drawing. Application December 22, 1950, Serial No. 202,436

This invention relates to an improved method for emulsifying liquid polymerizable compounds, and foreffecting polymerization of the compounds to form a stable emulsion of the polymer solids.

Polymerization in aqueous emulsion has lon been recognized as a particularly advantageous method. It has been customary in preparing the aqueous emulsion of a polymerizable compound to add the compound to water containing the desired amount of emulsifier and then vigorously agitating the mixture so as to form an emulsion wherein water constitutes the mntinuous phase.

The emulsions prepared according to this method have the monomeric itolymerizsble compound dispersed in globules of a preciable size throughout the water phase. When such an emulsion is polymerized, the resulting latex containing the emulsified solid polymer is poor in stability and tends to coagulate easily.

One improved method of forming more stable However. stability is not t e only climacteri tic essent nl'to a wood nol r-"er dis ersion It is eoual y desirable t at su h r fltnx' w en for ulated with other coat rv inere li nts. sho ld ex ib t a minimum of f om nr: durinw it" p licatien to surfaces in the orm of coatin s' and paints and in the pro u t on of films. Blisters and blemishes commonl occur as a res lt of fonmina during application o the formulated latex by brushing or snrayine when the latex employed is repared by methods l'nown in the prior art. Foaming durin a plifcation is generallvdue to .the presence of toolargev an amount of an emulsifier of a certain class in the latex composition. Emulsifiers of theclassthat are especially effective for thepurpose of'invertins:

a water-in-oil (monomer) emuls on to an oil monomer)-in-water ernvlsion upon. addition of sufficient water, are tliennes i'nmt likely to cause foaming when present in amounts of 0.5 per cent or more, by weight of monomer. However, with amounts of less than 0.5 per cent, foaming is decreased but stability of the final latex is also decreased. Furthermore, when such small quantitles of emulsifier are employed, inversion of the emulsion takes place with some difficulty, often requiring one to two hours of vigorous agitation before inversion occurs.

It is therefore an object of this invention to provide a method of producing stable aqueous dispersions of solid polymers which dispersions exhibit a minimum tendency to foam. Another object is to provide a. method of emulsifying polymerizable compounds whereby inversion of the water-in-monomer emulsion to the monomerin-water emulsion upon addition of sufiicient water, occurs immediately on agitation of the emulsion. A further object is to provide a method whereby polymerizable compounds are efliciently and advantageously emulsified to form a stable latex upon polymerization. Other objects will appear hereinafter.

It has been found that the foregoing and related objects may be attained, according to the method of the present invention. The first step of the new method consists in forming a waterin-monomer emulsion by uniformly mixing with agitation, at very small amount of water and of an anionic emulsifier with a predominant proportion of a polymerizable liquid monomer which is substantially immiscible with water. The proportions to be employed are definedhereinafter. When the water-in-monomer emulsion is formed, agitation is interrupted. There is then added to the emulsion sufficient water containin r a larger amount of another emls fier (a able of disnersin'! polymeric solids, so that upon subse uent, visorous agitation, an aoueous emulsion of the monomer is formed herein water constitutes the continuous phase. The resulting aoueous emulsion is subjected to the'usual polymerizing conditions of time, temperature and catalyst so that lieuid monomer therein is converted to solid polymer.

he proportions of water and of anionic emulsifler which are admixed with the monomer in order to obtain a water-in-rsonomer emulsion, are a diusted to re resent an aqueous solution containing at'least 5 per cent by weight of the emulsifier. Water-emulsifier ratios representing solutions of about 10 to 60 per cent by weight ofthe emulsifier. are preferred. The optimum concentration will vary to some extent as determined by the particular emulsifying agent and delayed for as long as 30 to 90 minutes.

the .method of the present invention effects a .invert communes-m.

based on the weight of monomer, is generally employed in the aqueous phase.

In the step of adding water to the water-inmonomer emulsion for purposes of inversion, a

second emulsifier is present in :the water being:

added, in an amount somewhat larger thanthat oi the first. An amount of about 0.5 to 8 per cent and preferably 4 per cent of the second-stage emulsifier, based on the weight of monomer, is

used. The second emulsifier should be one which is capable of effectively dispersing solids formed during polymerization but which is characterized by low foaming: tendencies.

The additionof the watersolution to the waterin-monomer emulsion "may be effected in any suitable manner and in such an amount as to obtain any desired monomer concentration for polymerization purposes. At least a suilicient amount of the water solution of emulsifier is added-that upon subsequent agitationan aqueous emulsion of the monomer is formed wherein water constitutes the continuous phase. The step of discontinuing agitation before the water soluticnof ths'second-step emulsifier isadded to the .water-in-monomer emulsion, is a very critical'one in the new process. In comparable experiments, it. has been found that surprising, unexpected,

and totally different results are obtained when the same quantities of water are added to two identically-prepared water-in-monomer emulsions, containing less than 0.5 per cent of the first-step emulsifier, but wherein-one emulsion is agitated vigorously during the addition of water ,While the other is not agitated until all the water has been added. In the latter method, inversion.to a monomer-in-wateremulsion occurs :im-

mediatelv, whereas in the method of agitatint; during the addition of water, inversion may be Thus significant saving of time. When amounts of thefirst-step emulsifier are greater than 0.5 per cent by weight of the monomer, the emulsions immediately upon. adding the water, whether or not agitation has been interrupted,

but an undesirable amount of foaming is observed when using the polymer dispersion, due

in the presence of too large an amount of the anionic emulsifier introduced in the first step.

1 The preparation of the water-in-monomer :cmu-lsions of the invention is effected without heatinrr, and such normal and convenient tern reratures as 10 C. to C. may be used. In

hose cases where the monomers employed are .ueous at those temperatures, it will be nece ;ary tonpply superatmospheric pressures in order to maintain the monomers in liquid phase.

The process of the invention may be applied to preparation of stable emulsions of any. substantially water-insoluble polymerizable monoethylenically unsaturated liquid compound.

lchanical stirrer.

'suchflas 'vinyl acetate; 'vinylldene chloride; vinyl aromatic compounds like styrene; acry'late and m'cthacrylate esters; unsaturated nitriles "such as,

a-crylonitrile; vinyl ketones suchas rmethyl vinyl or methyl :isoprppenyl ketone; as well as similar. singly olefinic compounds.

The following exampleis'given forthe purpose ofillustrating the practice of the invention;

, p Example A 200 ,gal1on kettle was c'hargedwith 6715 pounds of vinylidene chloride, 118.5 pounds of.

acr'ylonitrile, and 210 pounds of dibutylphthalate. The charge was mixed thoroughly with a mewhich was a petroleum hydrocarbon sodium vsulphonate (Alkanol WXN) ,was added with agitation to form .a water-i'n-cil emulsion with the monomers and plasticizer. :Agitation was then discontinued. fl'oyth'e emulsion was added 820 pounds ofwater 'rcontaining '30 pounds of the sodium salt of the "formaldehyde condensation product of naphthalene sulphonic acid (Daxad .11), "1.9 pounds of a commercial. per cent hydrogen peroxide solution, and 110 grams of a 6 per cent ferric ni rate solution. Subsequently r of emulsion.

agitation of the contents of the kettle was resumed, whereupon inversion occurred with the.

formation of an oil-imwatcr type emulsion. Air

Iv-sas .displac'edin thcket'tle and polymerizationof :the monomers proceeded at 4'5 0. for 22 hours.

At the end of this time, the conversion to the copolymer, based on total monomers charged to the system, wasabout 'to per cent by weight. The latex product thus Iormed'contained 52.4 per cent solids. The later; ap :eared to be 'well dispersed with very'little deposition of solid polycnts into a-single aqueous solution-containing all of the emulsifying: agents, the proportions being those of the preceding exampldanrl'the resulting oil-in\vater emulsion was polymerized, .a latex was formed which deposited at least '4 timesas much polymer on the walls of the reaction'vcssel as did the emulsion of the erample. Themechanical stability of the later was tested .in the same manner as the latex above, and coagulation was noticeable in 41 minutes of stirring. Thus, the method of the present invention produced :a later that was more than .iour times .as stable as the one obtained by a method of "the prior art. I

Other latices method described were prepared according to the in the example, differing only in that more than 0.5 pcr cent of activcportion of Alkanol .WXN, based on the weiuh't of monomers, was used to form the water-in-oil type The latices thus obtained, after polymerization, were :as stable as that of the ex.- ample but foamed considerably during the mochanical stability test, or when the emulsions were used in coating operations.

While the invention has been described .with respect to the copolymer of vinylidene chloride and acrylonitrile, it may be applied as Well to any About 2.5 pounds of a .50 per 'cent aqueous solution. of an anionic emulsifier,

of the substantially water-insoluble liquid monomers previously identified.

Among the anionic emulsifiers that are useful in forming the water-in-monomer emulsion of the first step of the present process, are those known by the commercial names: Alkanol WXN (a petroleum hydrocarbon sodium sulphonate), Santomerse D (a decyl benzene sodium sulphonate), Duponal ME (a sodium lauryl sulphate), Nacconal HG (an alkyl aryl sulphonate), Aquarex D (a sodium lauryl sulphate), and Aerosol MA (a dihexyl ester of sodium sulphosuccinic acid). When used in amounts sufficient to keep polymer solids in dispersion,

these emulsifiers are characterized by a tendency to form emulsions that foam excessively.

Among the emulsifiers that are useful in dispersing polymeric solids in the second step of the present process, are those known by the commercial names: Daxad 11 (a sodium salt of the formaldehyde condensation product of naphthalene sulphonic acid), Oronite (an alkyl aryl sodium sulphonate), Detanol (a sodium salt of an alkyl sulphonate), and Alkanol B (a sodium allzyl naphthalene sulphonate). emulsifiers are good dispersants of polymeric solids but are poor monomer dispersants and have relatively little tendency toward foam for: mation in emulsions.

I claim:

1. The method which comprises forming with agitation a uniform mixture of a substantially water-insoluble polymerizable mono-ethylenically unsaturated liquid monomer with about 0.05 to 0.4 per cent, based on the weight of monomer, of an anionic emulsifier, dissolved in sufiicient water to form a 5 to 60 per cent solution of the emulsifier, the emulsifier being one which is capable of forming water-in-monomer emulsions and which is incapable at any concentration of maintaining polymer solids in nonfoaming dispersions and being selected from the class consisting of sodium salts of petroleum hydrocarbon sulphonic acids, of decyl benzene sulphonic acids, of lauryl sulphuric acid and of dihexyl esters of sulp-hosuccinic acid; discontinuing agitation when a water-in-monomer emulsion has formed; adding to the quiescent emulsion sufficient water containing about 0.5 to 8 per cent, based on the weight of monomer, of

an emulsifier, of a different type from the first, which is a poor dispersant for liquid monomers but is capable of dispersing polymer solids without significant foaming and is selected from the class consisting of sodium salts of alkyl sulphon- 2. The method as claimed in claim 1 wherein the polymerizable monomer comprises vinylidene chloride.

These '3. The method as claimed in claim 1 wherein the polymerizable liquid compound is a mixture of vinylidene chloride and acrylonitrile.

4. The method as claimed in claim 1 wherein there is employed about 0.1 to 0.15 per cent, based on the weight of monomer, of the anionic emulsifier, capable of forming the water-inmonomer emulsion.

5.'The method ascIaimed in claim 1 wherein there'is employed about 4 per cent,-based on the weight of monomer. of the emulsifier capable of dispersing polymericsolids.

6. The method which comprises forming with agitation a uniform monomeric mixture of per cent vinylidene chloride and 15 per cent acrylonitrile with about 0.1 to 0.15 per cent. based on the weight of monomers, of an anionic emulsifier in the form of a 10 to 60 per cent aqueous solution, the emulsifier being one which is capable of forming water-in-monomer emulsions and which is incapable at any concentration of maintaining polymer solids in nonfoaming dispersions and being selected from the class consisting of sodium salts of petroleum hydrocarbon sulphonic acids, of decyl benzene sulphonic acids, of lauryl sulfuric acid and c1! naphthalene sulphonic acids, so that upon sub-,

sequent, vigorous agitation, an aqueous emulsion is formed wherein water is the continuous phase; agitating the mixture to form a monomer-in-water emulsion; and subjecting the resulting aqueous emulsion to polymerizing conditions to convert the liquid monomers to a solid vinylidene chloride-acrylonitrile copolymer.

7. The method as claimed in claim 6 wherein the anionic emulsifier employed in making the Water-in-monomer emulsion is the sodium salt of a petroleum hydrocarbon sulphonate.

8. The method as claimed in claim 6 wherein the emulsifier, capable of dispersing polymeric solids, is the sodium salt of the formaldehyde condensation product of naphthalene sulphonic acid.

9. The method as claimed in claim 6 wherein the anionic emulsifier employed in making the water-in-monomer emulsion is the sodium salt of a petroleum hydrocarbon sulphonate and the emulsifier capable of dispersing polymeric solids is the sodium salt of the formaldehyde condensation product of naphthalene sulphonic acid.

JACK J. ADAMS.

Number Name Date Kolvoort et al. Aug. 16 194D 

1. THE METHOD WHICH COMPRISES FORMING WITH AGITATION A UNIFORM MIXTURE OF A SUBSTANTIALLY WATER-INSOLUBLE POLYMERIZABLE MONO-ETHYLENICALLY UNSATURATED LIQUID MONOMER WITH ABOUT 0.05 TO 0.4 PER CENT, BASED ON THE WEIGHT OF MONOMER, OF AN ANIONIC EMULSIFIER, DISSOLVED IN SUFFICIENT WATER TO FORM A 5 TO 60 PER CENT SOLUTION OF THE EMULSIFIER, THE EMULSIFIER BEING ONE WHICH IS CAPABLE OF FORMING WATER-IN-MONOMER EMULSIONS AND WHICH IS INCAPABLE AT ANY CONCENTRATION OF MAINTAINING POLYMER SOLIDS IN NONFOAMING DISPERSIONS AND BEING SELECTED FROM THE CLASS CONSISTING OF SODIUM SALTS OF PETROLEUM HYDROCARBON SULPHONIC ACIDS, OF DECYL BENZENE SULPHONIC ACIDS, OF LAURYL SULPHURIC ACID AND OF DIHEXYL ESTERS OF SULPHOSUCCINIC ACID; DISCONTINUING AGITATION WHEN A WATER-IN-MONOMER EMULSION HAS FORMED; ADDING TO THE QUIESCENT EMULSION SUFFICIENT WATER CONTAINING ABOUT 0.5 TO 8 PER CENT, BASED ON THE WEIGHT OF MONOMER, OF AN EMULSIFER, OF A DIFFERENT TYPE FROM THE FIRST, WHICH IS A POOR DISPERSANT FOR LIQUID MONOMERS BUT IS CAPABLE OF DISPERSING POLYMER SOLIDS WITHOUT SIGNIFICANT FOAMING AND IS SELECTED FROM THE CLASS CONSISTING OF SODIUM SALTS OF ALKYL SULPHONIC ACIDS, OF ALKYL NAPHTHALENE SULPHONIC ACIDS, AND OF FORMALDEHYDE CONDENSATION PRODUCTS OF NAPHTHALENE SULPHONIC ACIDS, SO THAT UPON SUBSEQUENT, VIGOROUS AGITATION, AN AQUEOUS EMULSION IS FORMED WHEREIN WATER IS THE CONTINUOUS PHASE; AGITATING THE MIXTURE TO FORM A MONOMER-IN-WATER EMULSION; AND SUBJECTING THE RESULTING AQUEOUS EMULSION TO POLYMERIZING CONDITIONS TO CONVERT THE LIQUID MONOMER TO SOLID POLYMER. 